Increasing throughput in additive manufacturing using a rotating build platform

ABSTRACT

An additive manufacturing technique uses digital mask-based illumination and a polar-based build environment for increased throughput. In one embodiment, the build environment comprises a rotating element having a surface. A coater is configured to deposit photopolymer material on the rotating element at a given flow rate. As the element rotates and the coater deposits the photopolymer material, a radiation source of an image scanning system projects an array of point sources (an image) onto the photopolymer material for an exposure time to cure a given layer. As the photopolymer material is deposited layer-upon-layer, and for each layer, a control system adjusts a relative position of the coater with respect to the surface, adjusts a speed of rotation of the rotating element, and maintains the flow rate and the exposure time constant.

STATEMENT REGARDING SPONSORED RESEARCH

This invention was made with government support under Contract No.1938466 awarded by the National Science Foundation. The government hascertain rights in the invention.

BACKGROUND Technical Field

This application relates generally to additive manufacturing techniques.

Brief Description of the Related Art

Stereolithography is a form of three-dimensional (3D) printingtechnology used for creating models, prototypes, patterns and productionparts in a layer by layer fashion (so-called “additive manufacturing”)using photo-polymerization, a process by which light causes chains ofmolecules to link, forming polymers. Those polymers then make up thebody of a three-dimensional solid. Typically, an additive manufacturingprocess uses a build platform having a build tray submerged in a liquidphotosensitive material. A 3D model of the item to be manufactured isimported into an associated 3D printer software, which software slicesthe 3D model into 2D images that are then projected onto the buildplatform to expose the photopolymer.

While additive manufacturing techniques have proven to producesatisfactory results, they have certain limitations that have preventedtheir widespread use for general manufacturing. One such problem is lowthroughput. In particular, increasing printing resolution requiresshrinking the spot size used in an additive manufacturing process. Inlaser-based stereolithography, this is the laser spot size on the buildsurface. In DLP based photopolymerization systems, the spot size refersto the individual micromirror pixel pitch used in the array. Shrinkingthe spot size reduces printer throughput by a factor of x². For example,reducing the spot size from 100 um (common in the industry) to 20 um isa factor of 5× reduction of the diameter. The area throughput, however,is 25× lower (5²). So, if it takes one (1) day to print a part with 100um spot size, then it will take 25 days to print the same part with 20um spot size resolution.

BRIEF SUMMARY

According to this disclosure, throughput of an additive manufacturingprocess is significantly increased by increasing the effectiveresolution of a large spot size with a digital mask, and providing animage scanning system to move that image across the build area. Theimage scanning system may be a digital micromirror device (DMD) array.In addition, in lieu of using a cartesian-based build platform thatmoves up or down with respect to the radiation source, preferably thehigh-throughput foam printing herein is based on continuous printingonto a polar-based rotating cylinder platform. The combination of thesetechniques allows high throughput due to the large spot size, but stillmaintains high spatial resolution.

In particular, and in one embodiment, a build environment comprises arotating element having a surface. A coater is configured to depositphotopolymer material (e.g., radiation-curable foam) on the rotatingelement at a given flow rate. As the element rotates and the coaterdeposits the photopolymer material (layer-upon-layer), a radiationsource of the image scanning system projects an array of point sources(an image or pattern) onto the photopolymer material for an exposuretime to cure a given layer. As the photopolymer material is depositedlayer-upon-layer, and for each layer, a control system adjusts arelative position of the coater with respect to the surface, adjusts aspeed of rotation of the rotating element, and maintains the flow rateand the exposure time constant.

The foregoing has outlined some of the more pertinent features of thesubject matter. These features should be construed to be merelyillustrative. Many other beneficial results can be attained by applyingthe disclosed subject matter in a different manner or by modifying thesubject matter as will be described.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the subject matter and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a chart comparing throughputs of known prior art techniquesversus the digital micromirror device (DMD) array technique of thisdisclosure;

FIG. 2 depicts an embodiment of an additive manufacturing systemaccording to the principles of this disclosure;

FIG. 3 depicts an illumination path that is implemented in an embodimentof the additive manufacturing system of FIG. 2 using a moving mirrorsystem;

FIG. 4 depicts a high-throughput foam printing method based oncontinuous printing onto a rotating cylinder platform according to thisdisclosure;

FIG. 5 is a simplified depiction of a roll-on-roll additivemanufacturing printing apparatus according to this disclosure;

FIG. 6 is a detailed perspective view of a first embodiment of a highthroughput, high resolution printer of this disclosure;

FIG. 7 depicts another view of the printer showing the various motionstages in additional detail;

FIG. 8 depicts several of the imaging system elements of the printer;

FIG. 9 depicts a second embodiment of the printer;

FIG. 10 depicts a structure of a backing sheet;

FIG. 11 depicts the backing sheet provisioned on the rotating drum infurther detail;

FIG. 12a depicts a schematic diagram for foam patterning using a DLPprojector source according to the techniques described herein;

FIG. 12b is a top-down view of the foam surface with image patterningdetails using the approach shown in FIG. 12 a;

FIG. 13a depicts a technique for point-wise patterning using a laserbeam with programmable modulation; and

FIG. 13b is a top-down view of the foam surface with image patterningdetails using the approach shown in FIG. 13 a.

DETAILED DESCRIPTION

The following presumes familiarity with vat photopolymerizationmanufacturing methods and systems. As is well-known, stereolithographyis a known technique for making solid objects by successively “printing”thin layers of a curable material, e.g., a radiation-curable material,one on top of the other. To this end, a programmed movable spot beam oflight (e.g., UV) shining on a surface or layer of radiation-curableliquid is used to form a solid cross-section of the object at thesurface of the liquid. The object is then moved, in a programmed manner,away from the liquid surface by the thickness of one layer and the nextcross-section is then formed and adhered to the immediately precedinglayer defining the object. This process is continued until the entireobject is formed. Using this printing approach, many different types ofobject forms can be created using the computer to help generate theprogrammed commands and to then send the program signals to thestereolithographic object forming subsystem.

According to this disclosure, an additive manufacturing method andsystem using a projected DMD array in lieu of a standard resolutionlaser spot size or a high resolution small laser spot size. The relativethroughputs are depicted in the chart shown in FIG. 1. As can be seenthe DMD array-based approach herein provides a significant throughputimprovement but without sacrificing resolution. As shown, and in oneembodiment, the DMD projects as an array of individual point sources,sometimes referred to as an “image” or “image pattern.”

A manufacturing system that implements the technique herein has variouscomponents. These include a radiation source for material processing.The radiation source may be an light emitting diode (LED), a laser diode(LD), a high intensity discharge lamp (HID), or the like. In addition,the system includes a digital mask, which is a subsystem used toselectively transmit or not (mask) radiation to the build surface.Examples include: DMD (e.g., a Texas Instruments® DLP chip), an LCDscreen, a micro-LED display (a so-called “direct display” device, whichis both the source and digital mask in such case), MEMS (micro electromechanical system), or the like. A direct display device is an array ofemitting devices that can be selectively illuminated creating an imagewithout the need for a separate light source (e.g., backlight) and mask.The manufacturing system also includes an optical system, which is aseries of optical elements required to shape, image and/or re-image themask used for selective curing of the material. The optical systemtypically comprises one or more collimating lenses, a beamexpander/reducer, and F-theta/field scan lens, and the like. Themanufacturing system also includes a scanning system, e.g., a movingmirror system that is used to reposition the image across the buildplate. Examples includes a polygon scanner, a galvanometer scanner, aresonant scanner, a galvo-resonant scanner, and combinations thereof.Finally, a build area where material is deposited and selectively curedis provided. The build area is polar. In the polar embodiment, layersare wrapped around a rotating axis continuously. This type of printingis sometimes referred to herein as “roll-on-roll.” The polar motionembodiment aims to further increase the speed of production. Thisembodiment uses a rotating substrate to accumulate material, which isselectively cured by the image scanning system. Because the rotatingsubstrate does not need to change directions like the cartesian motionembodiment, it can sustain much higher average processing speeds ascompared to existing photopolymer printing techniques.

FIG. 2 depicts the above-described components of the manufacturingsystem, in this case implementing using the polar-based buildenvironment.

FIG. 3 illustrates one embodiment depicting the digital mask (e.g.,Digital Light Processing (DLP) semiconductor DMD chip) 300 and how itinteracts with the moving mirror system 302 to control the illuminationpath of the UV light used to cure foam deposited on a rotating platform304. In an alternative, the polygon scanner shown in FIG. 3 is replacedwith galvo scanning mirrors.

FIG. 4 depicts additional details showing the build surface in anembodiment. In particular, a slot-die head 400 is shown depositing acontinuous layer of foam, which is then cured by UV illumination 402(from a radiation source) behind the slot-die head. In this embodiment,the slot die-coater and UV light are fixed, and the roller 404 spinscounter-clockwise underneath. The roller has a surface 405. Aphotopolymer layer (e.g., a radiation-curable foam) is shown on top of apreviously cured photopolymer structure 406. This method affords anumber of advantages over planar deposition embodiments, includingcontinuous fabrication, without sequential reset of layer and blade, andmore uniform control of time between deposition and curing.

As depicted in FIG. 4, the roller 404 spins counter-clockwise, but thisis not a requirement. In a variant embodiment, the roller spinsclockwise. In such case the layer is rotated (in almost one completerotation) before the imaging is applied.

The slot-die head 400 depicted in FIG. 4 is also representative of acoater, but it is not intended to be limited. The coater may be asprayer, a doctor blade, or the like.

With reference to FIG. 4, and in this embodiment, the printercontinuously deposits and cures layers (typically foam) to build athree-dimensional article layer-by-layer. This can be viewed as asteady-state process in a reference frame fixed with respect to theslot-die head 400. In particular, foam is dispensed through the slot-diehead at constant volume flux (flow rate) {dot over (Q)} whilemaintaining a constant gap spacing h_(gap) and surface speed u_(s). Thisresults in a uniform foam layer with equilibrium height h_(l)downstream, which is subsequently cured by UV patterning at thedownstream distance L.

During printing, and typically under programmed control, the slot-diehead is translated radially outwards to accommodate the accumulation ofprevious foam layers deposited on the roller. This motion depends on thethickness of the deposited layer h_(l) and the speed u_(s). The latteris simply the speed at the outer surface of the previously-deposited andcured foam layer(s), which have accumulated height h_(s) from the rollersurface at the location directly underneath the slot-die head. The speedu_(s) is related to the angular rotation rate {dot over (θ)} of theroller by the following relationship:

u _(s)=(R+h _(s)){dot over (θ)},

where R is the radius at the roller surface.

As explained, the system is controlled to maintain constant speed u_(s)and layer height h_(l), which prescribes a constant flow rate of foamthrough the slot-die head. In a representative implementation, thevolume flux {dot over (Q)} of foam through the slot-die head is suppledby volume displacement of a progressive cavity pump, although this isnot a limitation. Depending on the method of foam generation, the pumpmay be in direct contact with the foam, or otherwise a liquid resin thattransitions to a foam at a certain location along the conduit pathconnecting the pump and the slot-die (e.g., a resin with dissolved gasexpands into a foam at a specific location prior to exiting theslot-die) may be used. In any case, preferably the mass flux at the pumpand through the slot-die are equal during steady dispensing.

During printing, a control system (e.g., a microcontroller or computersystem under program control) is configured (i) to adjust a relativeposition of the coater and the image source with respect to the rollersurface (or the accumulated layers), and (ii) to adjust the speed ofrotation of the roller itself, in both respects continuously, as eachlayer is built, layer-by-layer. In this particular embodiment, therelative position control moves the coater and image source away fromthe roller, and the roller speed control slows the roller down withrespect to the speed in a prior rotation. In a further variant, and inlieu of moving the image source relative to the roller surface, avariable focus projector (or the like) may be used to adjust the focusof the image. Preferably, the position adjustments and rotation speedchanges are continuous as a particular layer is being printed (asopposed to being carried out in a step-wise basis when a next layer isabout to be printed). As both the relative positioning of the coater andimage source components and the rotation speed are continuouslyadjusted, the control system maintains a constant flow of foam and aconstant exposure time.

At the conclusion of the printing process, uncured material is removedfrom the substrate (“cleaned and washed”), and then post-cured. One orboth of these operations are optional. The clean and wash may be carriedout in any manner including thermal, physical, pneumatic, or chemicalmeans. A thermal embodiment includes warming the material so that itsviscosity drops and allowing the uncured material to separate from thecured material, e.g., by gravity (drip dry). A physical post-processingmay include a spinning or rotating process that pulls uncured materialfrom the part using centripetal force (e.g., a spin dryer). A pneumaticpost-processing may use an air knife to help remove uncured materialfrom the cured matrix. A chemical post-processing may involve a chemicalor solvent bath to remove uncured material from the matrix.Post-processing operations may be carried out in any order.

Conventional vat photopolymerization techniques typically involveproducing layers of an article by additively combining cross-sectionalareas of a given height or layer thickness. Layers are deposited byrepeatedly raising and dipping an element into a large vat of material,with the layers then built on an XY plane, with height in the Z plane.The technique of this disclosure, in contrast, instead utilizes arotating element (a drum, typically cylindrical) onto which a thinphotopolymer layer is deposited, preferably across an entire width ofthe drum. After deposition, light is patterned onto the drum, partiallypolymerizing the polymer in a spatially and energetically precisemanner. As the printer drum rotates, a coating system and imaging systemare indexed away from the rotating drum by one layer thickness, thusallowing a next layer to be coated directly on top of the previouslayer. Printing layer-by-layer in this manner (“roll-on-roll”) typicallyis conducted continuously and with high material efficiency. The notionof “continuous” printing is not meant to foreclose circumstances wherethe print is stopped at a certain place to change materials, addexternal elements (inserts for electronics, mechanical assemblies,fasteners, and the like.

Following printing, the partially polymerized polymer (which may befoamed) is removed from the drum and uncured resin is removed and sentto a filter system for re-use in a subsequent print. This operation maybe carried out in an automated way using robotics. Due to the partiallypolymerized state of the material (e.g., gelation <60% cure), the oncecurved material can then be formed (e.g., laid flat), where a final curecan occur if necessary, e.g., as is the case with standard vatphotopolymerization. The gelation percentage will vary depending on thephotopolymer material employed, and certain materials may be suitablefor even lower gel points, such as 10%. Essentially, it is desired tocure (crosslink) the polymer enough so that it can hold the patternedshape and survive the print and post-cure, but still beflexible/compliant enough to unroll and mold to a final desired shape.Further, certain resin chemistries allow for a dark post-cure, which thereaction continues even after the light is turned off, and this approachmay be implemented here as well. This roll-on-roll approach also lendsitself to curing in an arbitrary position, such as in a layup tool ormold, or otherwise during manufacturing of a part. For example,partially cured sheets may be applied in situ onto some other existingstructural elements, where the full curing can then take effect. Anotherembodiment entails patterning layers at different degrees of gelationcure (e.g., one or more first layers at 60%, one or more later layers at90%) such that when the material is pulled from the roll, it exhibitsdifferent degrees of gelation within the same structure. In stillanother embodiment, layers are patterned with different degrees ofgelation cure, such that when the material is pulled from the roll itexhibits locally-controlled mechanical properties. Generalizing, andbecause a degree of curing of the photopolymer material depends on theamount of irradiating light, variations in light intensity or grayscalemay be used to control the degree of curing, and thus the mechanicalproperties, of localized areas or portions of the material.

FIG. 5 depicts a first embodiment of a printer apparatus 500 forroll-on-roll printing according to the above-described approach. Asshown, the apparatus 500 comprises a print bed 501 that includes arotary motor 502 for driving a rotating element, designated as rollerplatform 503. Typically, the roller platform 503 is cylindrical,although this is not required, as the platform may have other shapessuch as elliptical, polygonal, etc., and the platform may be symmetricalor asymmetrical in cross-section. The roller platform supports anarticle 505 that is being additively manufactured layer-by-layer. Whilethe first (initial) layer of the article may be made on the rollerplatform itself, preferably a backing sheet 506 is laid down initially(on the platform) and the article built on top of the backing sheet. Thebacking sheet may comprise a composite material, e.g., waxed on one sidethat supports the layer(s) being deposited, and unwaxed on the other.The backing sheet typically is designed for a single use; after thearticle is built, it is removed. The backing sheet, however, can bemulti-use. Inclusion of the backing sheet simplifies maintenance andthereby increases yield, as it obviates cleaning of the roller platformafter every use. The backing sheet may be configured to be positioned onthe platform discretely, or continuously, with the active portion of thebacking sheet then removed following removal of the article.

In this embodiment, a gantry 508 supports both a coating system 509, andan imaging system 511. As viewed in FIG. 5, the gantry moves forward orbackward to position the coating and imaging systems relative to theroller platform, which in this embodiment is stationary. The coatingsystem 509 comprises a resin reservoir 510, a pump 512, and a slot-die514. These elements are mounted on a support 515 that is movablelinearly up and down (in this view) with respect to the gantry 508 thatis moving forward or backward. As shown in this view, the slot die 514typically has the same length as the article being built. Thus, andalthough not depicted, typically the slot-die 514 is configured forlateral movement relative to the roller platform. The imaging system511, which includes a projector and scanner, generates an image pattern516 (focused or otherwise) that produces the desired pattern as theroller platform 503 rotates. In particular, as the roller platform 503rotates, the coating system 509 deposits a thin layer of photopolymermaterial across the width of the rotating drum and, after deposition,the imaging system 511 applies the image pattern 516 onto the drum. Aswas depicted in FIG. 4, the drum continues to rotate to form a newlayer, with the coating system and imaging system indexed (upwards inthis view) from the rotating roller platform by one layer thickness.There are two methods by which the system can move with respect to thecoater/projector and build surface: (i) discretely after each layer (ajump), or (ii) it can move continuously as the roller rotates (a scan),the latter being a preferred approach. After the article is builtlayer-by-layer in this manner, it is removed from the roller platform,and the backing sheet 506 (on which the article is built) discarded. Asnoted above, preferably the material is only partially polymerized, andthe rolled article is the unrolled or further processed as necessary.

FIGS. 6-7 depict the printer of FIG. 5 in additional detail. FIG. 6 is aperspective view, and FIG. 7 is a side (elevation). As shown in FIG. 7,the gantry 708 is supported on a coupling 718 that moves left to right(in this view) on a ball screw 720 driven by drive motor 722. Thecoating system (or “coater”) 709 and imaging system 711 are supported onan upstanding optical rail 724. A position of the coater 709 on the rail724 is adjustable by positioning a carriage 726; likewise, a position ofthe imaging system 711 on the rail is adjustable by positioning acarriage 728. In this embodiment, the relative positions of the coater709 and imaging system 711 with respect to one another remain fixed(during the print operation). After each layer is printed, a drive motor730 drives a ball screw 732 to index the optical rail 724 upwards sothat a next layer may then be deposited. Although not shown in thisview, both the coater 709 and imaging system 711 are also configured tomove in and out (relative to the view being depicted). FIG. 8 depictsthe components of the imaging system 811 when viewed from the front. Asshown, and in this embodiment, the imaging system 811 comprises ascanner 834, and a projector 836 that includes the DMD. The projector836 comprises mirrors 838 and 840, an X galvo 842, an Y galvo 844, andan output lens 845 (e.g., an f_(θ) lens) that corrects a field of viewof the image. The projector 836 comprises lens tube 846, whichcollimates or focuses the UV image produced by the projector. Theprojector tiles the image using the galvos/mirrors. While a lens tube isused, other optical elements (e.g., lenses, beam expanders, etc.) may beused for shaping, collimating, focusing and steering.

The 3-axis printer configuration depicted is not intended to be limited.In another embodiment, the coater and image projector are configured tomove independently of one another yet still relative to the fixedrotating drum. In this embodiment, the coater moves only in a Ydirection, and the projector moves in a Z direction.

In yet another embodiment, the coater and the image projector arethemselves fixed, with the roller platform then mounted for movement(e.g., in an Y direction) on a linear axis. This configuration isdepicted in a plan view in FIG. 9.

Generalizing, the technique of this disclosure provides forlayer-by-layer additive manufacture on a platform element that rotateswith respect to the coater and/or projector, with the relative positionsof the coater and/or the coater/projector being adjusted as a layer isbeing formed (a scan) or after each layer (a jump) of the article isformed. As has been described, it is not required that any particularcomponent (the rotating platform element, the coater, or the projector)be fixed, as long the relative movement of the components is achieved.

An electronic control system is used to control the operation of theprinter. To this end, one or more computers (e.g., servers, networkhosts, client computers, integrated circuits, microcontrollers,controllers, field-programmable-gate arrays, personal computers, digitalcomputers, driver circuits, or analog computers) are programmed orspecially adapted to perform control tasks, such as: controlling theoperation of, or interfacing with, hardware components of the printersystem, including the digital micromirror device (DMD), motors, pumps,valves, and sensors; creating or accessing a digital representation ofan object to be fabricated and, based on this digital representation, tocontrol shapes of spatial light patterns projected by the DMD tofabricate the object by photocuring; as depicted in FIG. 4, controllingmotion of the rotating platform and synchronizing this motion withprojected light images, e.g., by controlling timing of steps taken bystepper motors and timing of images projected by a DMD; receiving datafrom, controlling, or interfacing with one or more sensors; andperforming other calculations, computations, programs, algorithms, orcomputer functions as necessary to facilitate control over theabove-described printer or process. For example, software in the controlsystem enables real-time relative positioning of the rotating platform,coater and projector to ensure that the projected light hits andpenetrates the layer surface in a precise manner to ensure properformation of the layer. One or more thermal cameras may be used forthermal measurement to facilitate software-driven compensationtechniques for photopolymerization. In lieu of thermal cameras, aphoto-fluorescent dye may be used with a regular camera (e.g., a CMOS-,or CCD-based camera) to enable the control system to quantify how muchlight is exposed on the photopolymer and then make adjustments withrespect to the next layer being printed. As a further variant, real-timelayer measurement is implemented with axial laser intensitymeasurements. In this approach, a laser with a large spot size is set upon one end of the roller and at the edge of the slot die coater, and itis aimed at a receiver on the opposite edge of the roller. Intensitymeasurements are then used as real-time feedback for layer height/gapheight. Similarly, a laser displacement sensor, or other thicknessmeasurement device (e.g., an ultrasonic sensor) may be used to obtaincoating thickness measurements and make adjustments during the printing,process.

Generalizing, the above-described control system ensures that therotating platform operates continuously as the article is made, slowingdown rotations and altering material deposition as the layersaccumulate. The control system also maintains a constant linear velocityof the surface of the roller relative to the coater as the layersaccumulate. As compared to known cartesian-based implementation, theprint operations themselves are carried out without starting orstopping, or changing directions.

As noted above, preferably the article is manufacturing on top of ahacking sheet (a substrate) that overlays the rotating element (therolling build surface), which is typically formed of metal (e.g.,aluminum, steel, stainless-steel, etc.) or a composite (e.g.,fiberglass, or carbon fiber). Fla 10 depicts a cross-sectional view ofthe preferred structure of the hacking sheet, which acts as a processingaid with “quick release” properties that facilitates quick change oversbetween prints. As depicted, the product comprising a filament tape 1000used to release the print. The paper 1002 is waxed on one side. Freezerpaper may be used for this purpose. The waxed side has an adhesive edge1004 on both ends to adhere it to the printing cylinder. In an exampleembodiment, a 12″ long piece of filament tape (e.g., 3M knifeless tape“design line”) is placed in a III-shape on an aluminum roller. The shapeis 7.5″ wide by 2″ tall. A 7.5″×12.5″ sheet of freezer paper is used asthe hacking paper; as noted, the paper is waxed on one side. The edgesof the waxed side are coated with a ¼″ wide glue stick adhesive toadhere the edges down to the aluminum cylinder. The paper is 90 micronsthick, and the filament tape is less than 100 microns. When printing isfinished, the design line is used to separate the sheet from thealuminum cylinder, and a new sheet is then configured. FIG. 11 depictsthe drum with the hacking sheet affixed.

In an alternative embodiment, the backing sheet is applied from a rolland in an automated process.

Because printing does not require starting, stopping or changingdirections of the build platform, the printer can operate continuouslyduring the actual print operations. This enables large articles to beprinted on the drum at high speed, and preferably up to a low gel point(e.g., in the range 10-60% cross-linking depending on the material).Upon removal, a final curing (flat or in a mold) is then carried out toa verified state (>90% cross-linking cure). In addition, and after anyuncured resin is removed, other post-processing may be carried out. Onepost-processing technique that may be used to remove uncured resininvolves heating the material, causing the liquid foams to rapidlydecrease viscosity, and then letting them drain. Heating may be carriedout with convection, conduction or radiation (e.g., microware or RF).Draining can occur either naturally by gravity, pneumatically with anair-knife curtain, by vacuum, or mechanically with a spin-dry cycle.

The printer may be used to make an out-of-round object concentric.

Different materials may be applied by the coater for different layers ofthe article.

FIGS. 12a-b depict a schematic diagram for foam patterning using a DLPprojector source according to the techniques described herein. FIG. 12aillustrates a projected image focused to a region on the foam surface bya lens (e.g., 845 in FIG. 8), and line scans are performed by rotationof galvo mirrors (only one is shown); FIG. 12b is a top-down view of thefoam surface with image patterning details. In this example embodiment,the foam resin is patterned using a DLP projector 1200 and UV lightsource, which emits a rectangular N_(x)×N_(y) pixel image, noted inreference to the {circumflex over (x)}×ŷ projector coordinates withrespect to the foam's surface (FIG. 12b ). The image path is positionedby reflection from two galvo mirrors (mirror 1202 is shown) before itpasses through the f_(θ) lens 1204 (or other scanning, lens, lens arrayor system) and focuses onto the foam. Each galvo mirror iscomputer-controlled and rotates about one axis; these axes areperpendicular to one another and correspond to steering the bean byangles θ_(x) and θ_(y) with respect to the normal coordinate of the foamsurface (i.e., a {circumflex over (z)}-direction in FIG. 12b ). Thef_(θ) lens works by converting the incident angle of the image path intoa translation of the image focal point from the lens center, scaled bythe focal length f, i.e.

x _(f) =fθ _(x)

x _(f) =fθ _(y).

The result is an image projected onto the foam centered at coordinate(x_(f), y_(f)) with rectangular area A_(DLP)=N_(x)N_(y)D² where D is thepixel size. A large-area pattern is created by translating the imageacross the foam in discrete steps per frame exposure.

Another approach to patterning is point-wise patterning. As depicted inFIG. 13a-b , the foam resin is patterned using a UV laser beam withprogrammable modulation. FIG. 13a depicts a modulated laser beam focusedto a spot on the foam surface by the lens, and line scans are enabled byrotation of a polygonal mirror 1302; FIG. 13b depicts a top-down view ofthe foam surface with laser patterning details. The pattern ofmodulation for the laser beam changes the laser spot intensity over thecourse of traversing each scan line to create the desired pattern. Twoembodiments for generating the modulated laser beam are: (i) acontinuous UV laser beam passed through an electro-optic modulator 1300,which programmatically modulates the laser beam intensity from 0-100%;and (ii) a UV laser diode (not shown) modulated on or off by anintegrated circuit processor. The former approach enables higher laserpowers and greyscale capability, however, the modulation rate istypically slow compared to the later. Patterning resolution isdetermined by the lasers focused spot diameter D. and the fractionaloverlap of the spot diameter per modulated exposure in the x and ydirections, namely, η_(Δx), η_(Δy), respectively (FIG. 13b ). The lasertraverses the foam in x-direction scan lines at speed {dot over (x)}_(f)and the foam translates in the y-direction at speed U; each row oflength w is patterned sequentially and in time t_(w).

As noted above, the above-described printing techniques may comprise afront-end of a system that includes various types of post-processing.The following provides additional details regarding post-processingoptions. For example, after accumulation of the material and patterningis complete, the patterned material may be taken off the roll, cleanedand cured. As previously noted, the order of the post-processingoperations may vary depending on the end goal of the processing. Removalmay involve dissolving glue that binds the sheet to the roller, or, ifglue is not used, having a pull strip. Another approach to removal isproviding a vacuum source in association with the rotating cylinder thatsucks down the paper, with the vacuum then being turned off when removalfrom the cylinder is complete. A blower may then push the paper off theroll, e.g., and onto a conveyor belt. An alternative to applying avacuum may be to apply heat, and then blowing the material off. Cleaningmay involve chemical approaches (e.g., a solvent bath), using anair-knife, applying a thermal source, or using a mechanical technique (aspin dry). Curing may include a light bath, a secondary cure using heat,or using an RF source. The post-processing may comprise part of anend-to-end system that includes the patterning.

As also mentioned, it is known in the art that, when curingphotopolymers, the degree of cure of a photopolymer can be varied by theamount of light irradiation dose. Therefore, it is possible to use lightintensity to control the degree of cure, and this controls themechanical properties of a printed article. This technique can becombined with the subject matter described to fabricate afunctionally-graded article with tuned mechanical properties. A combinedtechnique of this type then provides a notion of 4D printing (with 3Dbeing shape and the added dimension being time). In this approach, thedegree of cure of different layers throughout the article is varied atthe voxel level. This allows multi-material-like properties within thesame printed piece, using the same material (although using differentmaterials on the same build is also within the scope). This allows theprinted article to account for things like shape memory effects or toencourage different shapes post-printing, e.g., as activated bytemperature, moisture, light, or the like. A 4D printing approach alsoaligns naturally with the approach herein as printed materials willnaturally have a curl to them, due to being printed on a rotatingelement.

Generalizing, different layers may exhibit differing degrees of cure.For example, a top layer may have a 90% cure, whereas an underlyinglayer may have a 30% cure. By leveraging differing cure rates across oneor more layers, the resulting structure can be readily folded into adesired shape during post-processing.

The techniques herein may also be used in combination with volumetricprinting. Volumetric printing concurrently prints all points of a3-dimensional object by illuminating a rotating volume of photosensitivematerial within a transparent container at specific points and atvarying light intensities and at differing angles. In the combinedapproach, volumetric-like printing (e.g., involving multiple pointsources at varying light intensities and/or angles) concurrently cureall points of a 3D object within the material deposited on the roller.For example, optical projections provided at a plurality of angles andwith calculated 3D intensity distribution act over a fixed temporalexposure period to selectively cure portions of the photopolymer. Thisis carried out on individual layers, or across multiple layers of thebuild. In this manner, volumetric printing and the technique herein arecombined, on a layer-by-layer basis (or otherwise across multiplelayers), to fabricate an article composed of multiplevolumetrically-printed layers or regions.

Preferably, and when the photopolymer is a radiation-curable foam, thefoam dispensing is carried out in an automated manner and “on-demand”(meaning the foam is produced “just-in-time” to facilitate the printingof the current layer while the foam remains stable), once again underprogram control, so that the layer(s) are built up in a continuousmanner.

The material being printed may be a photopolymer that includes acomposite material filler. Representative filler materials includeceramics, metals, organic carbon fibers, and other organic or inorganicmaterials.

While the above describes a particular order of operations performed bycertain embodiments of the described subject matter, it should beunderstood that such order is exemplary, as alternative embodiments mayperform the operations in a different order, combine certain operations,overlap certain operations, or the like. References in the specificationto a given embodiment indicate that the embodiment described may includea particular feature, structure, or characteristic, but every embodimentmay not necessarily include the particular feature, structure, orcharacteristic.

While the disclosed subject matter has been described in the context ofa method or process, the subject matter also relates to apparatus forperforming the operations herein. This apparatus may be a particular 3Dprinting machine or system that is specially constructed for therequired purposes, or an existing commercial 3D printer that has beenadapted to print using the above-described foam and foam dispensingmechanism.

While the above description describes the system in the context offoamed materials, this is not a requirement as the techniques and systemmay be implemented using non-foamed materials.

Further, while the approach typically involves processing of liquidphotopolymers, solid and semi-solid photopolymers may also be used. Thismay be in the form of coating techniques using a liquid binder or directapplication of powders directly to the roll using a suitable coatingtechnique such as heat, light, static electricity or the like. Onceapplied to the rotating element, the material may be cured through lightradiation as previously described.

The techniques herein using a rotating build platform may also haveapplicability in other materials processing applications, includingnon-photopolymer materials such as powdered thermoplastics, ceramics,metals, composites thereof, and the like.

Depending on the desired size of the article being manufactured, it maybe desirable to position and use multiple printers or printer components(i.e., the optical system, the coating system, or otherwise) adjacent toone another in a continuous manufacturing process. For example, if thedesired workpiece is nine (9) feet in length and an output of a singleprinter is, e.g., three (3) feet in length, then the desired workpiecemay be formed by using three such machines in series.

What is claimed is as follows:
 1. A method of additive manufacturing an article, comprising: providing a rotating element having a surface; depositing photopolymer material on the rotating element at a given flow rate, the photopolymer material being deposited by a coater; after depositing a given layer, projecting an image onto the photopolymer material for an exposure time to cure the given layer; as the photopolymer material is deposited layer-upon-layer, and for each layer: (i) adjusting a relative position of the coater with respect to the surface; (ii) adjusting a speed of rotation of the rotating element; and (iii) maintaining constant the flow rate and the exposure time.
 2. The method as described in claim 1 wherein the coater is translated radially outward based on a thickness h_(l) of the given layer, and a speed u_(s) of the rotating element with respect to one or more previously-deposited and cured layers, wherein the one or more previously-deposited and cured layers have cumulative height h_(s) from the surface, and wherein the speed u_(s) is related to an angular rotation rate {dot over (θ)} of the rotating element by: u _(s)=(R+h _(s)){dot over (θ)}, where R is a radius of the rotating element at the surface.
 3. The method as described in claim 1 wherein the photopolymer material is a radiation-curable foam.
 4. The method as described in claim 1 wherein the photopolymer material is cured up to a low gel point.
 5. The method as described in claim 4 wherein the low gel point is between 10-60% gelation, and wherein the given state is greater than approximately 90% cross-linking.
 6. The method as described in claim 1 further including removing the article from the rotating element and continuing to cure the photopolymer material to a given state.
 7. The method as described in claim 6 further including: removing uncured photopolymer material; and applying a post-processing operation to cure the photopolymer material to the given state.
 8. The method as described in claim 7 wherein the photopolymer material is cured to the given state by flat curing or by curing in a mold.
 9. A high-throughput additive manufacturing system, comprising: a rotating element having a surface; a coater configured to deposit photopolymer material on the rotating element at a given flow rate; a radiation source that projects an image onto the photopolymer material for an exposure time to cure a given layer; and a control system that, as the photopolymer material is deposited layer-upon-layer, and for each layer: (i) adjusts a relative position of the coater with respect to the surface; (ii) adjusts a speed of rotation of the rotating element; and (iii) maintains constant the flow rate and the exposure time.
 10. The high-throughput additive manufacturing system as described in claim 9 wherein the coater is translated radially outward based on a thickness h_(l) of the given layer, and a speed u_(s) of the rotating element with respect to one or more previously-deposited and cured layers, wherein the one or more previously-deposited and cured layers have cumulative height h_(s) from the surface, and wherein the speed u_(s) is related to an angular rotation rate {dot over (θ)} of the rotating element by: u _(s)=(R+h _(s)){dot over (θ)}, where R is a radius of the rotating element at the surface.
 11. The high-throughput additive manufacturing system as described in claim 9 wherein the control system maintains a constant linear velocity of the surface of the rotating element relative to the coater as the layers accumulate.
 12. The high-throughput additive manufacturing system as described in claim 9 wherein the material is one of: a photopolymer, and a photopolymer comprising a composite material filler.
 13. The high-throughput additive manufacture system as described in claim 9 further including a digital mask that transmits UV illumination from the radiation source, and a scanning system that receives and applies the UV illumination as an image.
 14. The high-throughput additive manufacturing system as described in claim 13 wherein the digital mask is a digital micromirror device (DMD) and the scanning system is a moving mirror.
 15. The high-throughput additive manufacturing system as described in claim 9 further including a removable backing sheet supported on the rotating element.
 16. The high-throughput additive manufacturing system as described in claim 9 wherein the rotating element is configured as cylinder.
 17. The high-throughput additive manufacturing system as described in claim 9 wherein the rotating element is fixed and the coater and the radiation source are movable.
 18. The high-throughput additive manufacturing system as described in claim 9 wherein the coater and the radiation source move independently from one another.
 19. The high-throughput additive manufacturing system as described in claim 9 wherein the coater and the radiation source are fixed and the rotating element is movable.
 20. A method of additive manufacturing in a printing system comprising an element having a surface, a radiation source, and a coater having an outlet positioned adjacent the surface, comprising: as the element rotates, and while maintaining a constant flow rate from the outlet and a constant exposure time of the radiation source: depositing a first layer of photopolymer material on the surface; exposing a first image onto the first layer to cure the first layer; depositing a second layer of the photopolymer material on top of the cured first layer; and exposing a second image onto the second layer to cure the second layer; wherein a relative position of the outlet with respect to the surface, and wherein a speed of rotation of the element, are adjusted continuously during the depositing and exposing operations. 